Consider the union of the opaque regions of each RenderLayer in a backing when determining if the backing is opaque.
Make use of the Region::occluded() test from bug #72294 to reach this intermediate step, where we consider all relevant RenderLayers for a backing together. Next step: For each RenderLayer, we need to consider more than a single RenderObject and construct an opaque Region for the layer.
Created attachment 115020 [details] Patch
Created attachment 115822 [details] update for Region::contains()
Comment on attachment 115822 [details] update for Region::contains() Attachment 115822 [details] did not pass chromium-ews (chromium-xvfb): Output: http://queues.webkit.org/results/10374629 New failing tests: compositing/geometry/limit-layer-bounds-transformed.html compositing/iframes/enter-compositing-iframe.html compositing/iframes/connect-compositing-iframe.html compositing/geometry/clip.html compositing/geometry/fixed-position-composited-switch.html compositing/geometry/limit-layer-bounds-fixed-positioned.html compositing/geometry/limit-layer-bounds-positioned.html compositing/layer-creation/overlap-child-layer.html compositing/geometry/limit-layer-bounds-transformed-overflow.html compositing/geometry/limit-layer-bounds-positioned-transition.html compositing/layer-creation/overlap-transformed-layer.html compositing/layer-creation/translatez-overlap.html compositing/iframes/become-composited-nested-iframes.html compositing/geometry/limit-layer-bounds-overflow-root.html compositing/layer-creation/spanOverlapsCanvas.html compositing/geometry/limit-layer-bounds-clipping-ancestor.html compositing/layer-creation/overlap-clipping.html compositing/geometry/layer-due-to-layer-children-deep-switch.html compositing/iframes/connect-compositing-iframe-delayed.html compositing/layer-creation/overflow-scroll-overlap.html
Created attachment 115824 [details] Archive of layout-test-results from ec2-cr-linux-03 The attached test failures were seen while running run-webkit-tests on the chromium-ews. Bot: ec2-cr-linux-03 Port: Chromium Platform: Linux-2.6.35-28-virtual-x86_64-with-Ubuntu-10.10-maverick
Created attachment 115827 [details] Patch
Created attachment 116407 [details] Patch
Dropping this as bug #71972 will likely not happen, opting for more simple approach.